Chlorine is commonly used as a disinfectant and available as a gas, liquid or solid form dissolved in water. Common examples include sodium hypochlorite (liquid), calcium hypochlorite (solid), and lithium hypochlorite (solid). Additionally, chlorinated isocyanurates are a family of chemical compounds that, when in contact with water, release hypochlorous acid. Common examples include dichloroisocyanurate and trichloroisocyanurate. The amount of available chlorine differs between the forms, as shown:
Available ChlorineChemical(as HOCl)Chlorine Gas100% Sodium Hypochlorite Liquid 5 to 15%Lithium Hypochlorite Solid35%Calcium Hypochlorite Solid65 to 70%Sodium Dichloroisocyanurate Solid56 to 62%Trichloroisocyanurate Solid90%
Such chlorine disinfectants are commonly used to eliminate waterborne pathogens, including for example, enteric, pathogenic, and biofilm forming organisms. Waterborne pathogens can include: filamentous, corrosive, non-spore forming and/or spore forming bacteria; pathogenic bacteria, pathogenic viruses, parasitic protozoa, mycotoxins, algae, spore forming fungi/molds, yeasts and/or mollusks. However, there are known limitations associated with using chlorine sources as a disinfectant, including both stability and safety concerns. For example, chlorine gas is delivered in pressurized bulk containers. These containers range in size from rail tank cars and road tank trucks down to 150-lb cylinders. They are dangerous to handle and store and require compliance with strict handling and storage requirements and therefore are being phased out by certain government regulations (e.g. U.S. Department of Homeland Security Chemical Facility Anti-Terrorism Standards (CFATS)).
Liquid sodium hypochlorite (bleach) solutions present storage limitations as they tend to naturally decompose depending on the storage temperature, its age, concentration, and contaminants it may contain. The decomposition is accelerated upon exposure to sunlight, in addition to often containing caustic stabilizing agents.
There are also limitations associated with using solid chlorine compositions, such as pucks, tablets, pellets, and granular compositions. In particular, the solid compositions contain a lower amount of available chlorine and therefore a higher percentage of inert ingredients (e.g. stabilizers, binders, and salts). As a result, the delivered chlorine has an effect on water chemistry, including for example, alkalinity, water hardness, pH, total dissolved solids (TDS), total settable solids (TSS) and/or conductivity. In many instances, the effects or changes in water chemistry are not desirable as they can affect product quality, reaction efficiency, and/or process controls. For example: chlorine gas will decrease process water pH due to the hydrochloric acid produced when the chlorine gas is dissolved in the water; hydrochloric acid (HCl) will lower water pH; salt (NaCl) byproduct will increase conductivity or TDS in the process water; use of calcium hypochlorite, lithium hypochlorite, or chlorinated isocyanurates adds significant hardness and/or stabilizing and binding agents into water. Still further, chlorine used as a biocide results in generation of disinfection byproducts (DBP) due to the non-selective oxidation and substitution of chlorine species.
A further limitation of use of chlorine biocides involves the control reliability of processes using bleach solutions (e.g. 12.5%) due to natural bleach degradation pathways, wherein bleach forms sodium chloride (NaCl) and sodium chlorate (NaClO3) and the reaction rate increases with increasing temperature. Control reliability is also impacted by a second bleach degradation pathway, where trace metals (e.g. iron, nickel, copper, and cobalt form insoluble metal oxides) and light cause bleach to catalytically decompose to oxygen (O2) and sodium chloride (NaCl). This degradation results in a decrease in available free chlorine, off-gassing and by-product formation (e.g. chloride (Cl—) and chlorate (ClO3-) ions).
The use of chlorine bleach as an oxidant to form other biocides, such as chlorine dioxide, bromine, chloramine, iodine, and fluorine is known. However, the stability limitations associated with chlorine make it difficult to effectively and efficiency produce other biocides. For example, any chlorine forms used as oxidizing agents result in the natural degradation decreasing product concentration, production of a product with excess chloride ions leading to corrosion, producing acidic and/or unstable products, and/or resulting in a process that is unstable or dangerous to operate. Still further, chlorine sources with impurities (e.g. salts, stabilizers, binders) will result in biocide products with impurities. Accordingly, biocides produced from conventional reactions with chlorine are unpredictable without stable and pure chlorine. Therefore, there remains a need for methods of on-site generation of chlorine to resolve these stability issues and provide a chlorine source to overcome these limitations.
An object of the present invention provides methods for generating a stable source of chlorine to effectively and efficiently produce additional biocides.
A further object of the invention is to provide dual biocides at a point of use or onsite generation to overcome the stability and safety concerns with transporting biocides.
A still further object of the invention is to overcome stability and safety concerns associated with solid biocide chemistry, including reduced chemical handling concerns and elimination of risks associated with runaway chemical reactions involving solid biocides which are improperly fed and/or fed with incorrect feed equipment.
Still further, there remains a need for enhanced disinfecting formulations providing more effective disinfection due to resistance of pathogens. Therefore, an object of the present invention is to provide dual biocides (one or more) for enhanced disinfectant efficacy.
Other objects, advantages and features of the present invention will become apparent from the following specification taken in conjunction with the accompanying drawings.